FIELD OF THE INVENTION
This invention relates to the field of data communications, and more particularly to packet-based digital communications networks.
There are two broad classes of network: circuit-based and packet-based. Conventional telephone networks are circuit based. When a call is established in a circuit-based network, a hard-wired connection is set up between the calling parties and remains in place for the duration of the call. Circuit-based networks are wasteful of available bandwidth and lack flexibility.
Packet-based networks overcome many of the disadvantages of circuit-based networks. In a packet-based network, the data are assembled into packets containing one or more address fields which define the context of a packet, such as protocol type and relative positions of other fields embedded in the packet. LAN bridges and routers use the information in the packet to forward it to the destination.
In a packet-based network, a packet must be parsed as it flows through the network. Parsing is the process of extracting and analyzing the information, such as source and destination address and net layer protocol, contained in the packets.
In known networks, packet parsing is generally performed with a microprocessor, which provides flexibility in handling different packet types and can be upgraded to handle new packet types as they are defined. Content Addressable Memory (CAM) is commonly used for hardware assistance to speed up searches through a list of known addresses. This is a tedious task. CAMs are also relatively expensive and limited in size and availability.
General purpose processor architectures are not specifically directed toward the types of operations required in packet parsing and so they tend to be inefficient. To meet performance requirements, a fast but expensive processor based solution can be implemented. In the highest performance systems, hardware solutions are implemented to increase speed, but at the cost of flexibility.